A GaN-based crystal is known as being used for a short-wavelength light emitting device. Usually, the GaN-based crystal is formed by epitaxial growth on a sapphire substrate with a buffer layer being provided therebetween. If the GaN-based crystal is epitaxially grown directly on the Si substrate, a composite device including a light emitting device and a semiconductor integrated circuit may be produced.
A GaN-based crystal is available in two types. One type of GaN-based crystal has a wurtzite crystal structure having a superb piezoelectric characteristic, and the other type of GaN-based crystal has a zinc blende-type crystal structure which almost does not have any piezoelectric characteristic but has a high light emission characteristic, a high information transmission characteristic and a high information processing function. The differences in the crystal structure and the changes in the characteristics that are currently known are described in patent literature 1 (Patent Literature 1: Journal of Applied Physics (3675) Vol. 94, No. 6. I. Vurgaftman and J. R. Meyer; Band parameters for nitrogen-containing semiconductors) described later.
In general, a wurtzite crystal structure is a stable crystal structure. Meanwhile, a zinc blende-type crystal, which is metastable, promotes a superb carrier recombination and thus has a significantly high light emission efficiency. Therefore, the zinc blende-type crystal is strongly desired as a material of a light emitting element. The zinc blende-type crystal has the same structure as that of a GaAs crystal and an Si crystal.
Nanodots are reported in many papers as shown in patent literature 2 through patent literature 4 (Patent Literature 2: Journal of Crystal Growth, 255 (2003) 68-80 N. N. Ledentsov and D. Bimberg, “Growth of self-organized quantum dots for Optoelectronics applications: nanostructures, nanoepitaxy, defect engineering”, Patent Literature 3: Applied Physics letters 89, 161919 (2006) P. Rinke, et al., “Band Gap and band parameters of InN and GaN from quasiparticle energy calculations based on exact-exchange density-functional theory”, Patent Literature 4: Physica Status Solidi C6, No 52, S561-S564 (2009)/D0110.1002/pssc. 2008801913; Christian Tessarek et al., “Improved capping layer growth towards increased stability of InGaN quantum dots”).
In the case where Ga and In are grown in a miscible state, whether Ga and In are mixed in a crystalline state or not depends on the concentration ratio between Ga and In. Herein, a region in which Ga and In are not mixed together in a crystalline state is referred to as an “immiscibility gap”. Especially in the case where the crystal is grown at a low temperature or there is a large distortion remaining in the crystal substrate, there is a conspicuous tendency that whether an immiscibility gap is formed or not depends on the concentration ratio between Ga and In. Regarding the growth of Ga and In in a miscible state, all of the above-mentioned prior documents describes that gas is supplied in the immiscibility gap.
In a region having a growth temperature of 700° C. or lower and having an In concentration of 90% or higher, a uniform crystalline region containing the In element at a high content is grown. In this region, a quantum well (QW structure) may be formed as an active layer. However, the experimental results described in many documents are all regarding the wurtzite crystal. There is no experimental results on the cubic crystal (zinc blende-type crystal). Currently, no cubic crystal which may be technologically evaluated is available (Refer to Patent Literature 5: I. Ho and G. B. Stringfellow, Appl. Phys. Lett. 69, 2701 (1996), Patent Literature 6: PCT Japanese National-Phase Laid-Open Patent Publication No. 2011-523206, Patent Literature 7: Japanese Laid-Open Patent Publication No. 2011-3803, Patent Literature 8: Japanese Laid-Open Patent Publication No. 2011-44539, Patent Literature 9: Japanese Laid-Open Patent Publication No. 2010-245491)